pgsql: Doc: fix oversights in "Client/Server Character SetConversions"

Doc: fix oversights in "Client/Server Character Set Conversions" table.

This table claimed that JOHAB could be used as a server encoding, which
was true originally but hasn't been true since 8.3.  It also lacked
entries for EUC_JIS_2004 and SHIFT_JIS_2004.

JOHAB problem noted by Lars Kanis, the others by me.

Discussion: https://postgr.es/m/c0f514a1-b7a9-b9ea-1c02-c34aead56c06@greiz-reinsdorf.de

Branch
------
REL9_5_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/d368c6c711d03b8bb674274b2b3653985f305248

Modified Files
--------------
doc/src/sgml/charset.sgml | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)